Across:
   1,4ac. Sooner or later, Yes had foe: notes out of order! (3 2 5 4)
   4. see 1 across
   9. Public transport or cycling for Alphabet (3)
  10. Grant of bread mitigating allowance (5)
  11. Naked revel in source of toddy, bungalow verandah (5)
  12. Interfere with collection of 1 4 across, A 24 of 25, 3, 15 down, 21 and 6? (6)
  13. see 16
  15. As easily captured heart often does: like the odd prog rock composition? (5 5)
  16,13. Cut Jethro Tull frontman for South Carolina fellow who played blues with Blind Simmie Dooley (4 8)
  19. Sang about horses (4)
  20. Good number with sax intro in unison (10)
  22. Weaker one, pathetic deserter (little stamina in tight finishes) (8)
  24. Soft beheading of one that weeps, and soft spot where the weary head lands (6)
  27. Ray split from this union, abandoning what purists advocate (5)
  28. Do fly out for North Carolina Council that played blues with Blind Boy Fuller (5)
  29. Nobody heard sister (3)
  30. 26 in Oz's fantasy blows up (5 2 2)
  31. Swear to include piano in edgy bits (5)
Down:
   1. Voice claim only after cutting out odd bits, as this fellow would favour a simpler explanation (5)
   2. Personifying of God by me in performance (9)
   3. ELP's safer performing with no piano and with no worries about safety (8)
   4. Send out back for publican's shout? (4)
   5. Death of all ten in toxic spill (10)
   6. Genesis foe: too much music... one ends up repeating sounds (6)
   7. Relatives of colonial residents surrounding university (5)
   8. Nears 16 mess as air pushes it (9)
  14. If cleaning mess, it pushes air (7 3)
  15. 16 28 song of French town, but with Spanish introduction and motif in stanzas 1,3,4 and 5  (3 6)
  17. They get sucked in worse than snail (9)
  18. With ascending subsequence of Fibonacci, do I repeat at regular intervals? (8)
  21. Romney dog, oft mentioned by foes in Rush, essentially pursuing rich vein (6)
  23. Company controlling gas in capital (5)
  25. Using ascending thirds in most modes, King Crimson reworked airy movements (5)
  26. They say it has a dark side, a way of working and working (4)